Purification of high silicon iron alloys



Patented Nov. 10, 1942 UNITED STATES PATENT OFFICE 7 2,301,360PURIFICATION-0F men SILICON moN mors Joseph H. Brennan, Niagara Falls,N. Y., assignor to Electro Metallurgical Company, a. corpora.-

tion of West Virginia No Drawing. Application August 3, 1940,

Serial No. 351,125

I 3 Claims.

This invention relates to the purification of molten silicides andalloys containing a large proportion of silicon and refers moreparticularly to a process of removing calcium and aluminum from suchmolten silicides and alloys. The raw materials used in the production ofsilicides and such alloys as ferrosilicon frequently contain alumina andlime as impurities, and

when the usual manufacturing processes are pursued, using suchmaterials, the silicides or alloys produced are contaminated withaluminum and calcium. There is a demand, notably in the production ofelectrical steel sheet, for silicides and high silicon alloyspractically free from such contaminants, and to achievethe desiredpurity it has heretofore been necessary to use very pure grades of rawmaterials. These special raw materials are more expensive than theordinary materials utilized, and there is a demand for a methodutilizing cheaper grades of rawmaterials but at the same time producingsilicides or high silicon alloys containing little or no aluminum orcalcium. It is a principal object of this invention to'provide such amethod.

This object is achieved by the invention which comprises adding to amolten high silicon alloy or silicide produced in the usual way from theusual raw materials a quantity of a metal sulphide sufiicient to removealuminum and calcium. A preferred material for refining aluminum andcalcium from high silicon alloys is iron pyrites. If iron is anobjectionable impurity in the alloy or silicide being produced, nickelsulphide or cobalt sulphide or other appropriate sulphide may beemployed. The sulphide may a be added to the molten silicide or alloyeither in the ladle or in an auxiliary refining furnace. 1

In either event aluminum and calcium are removed in a fluid slag,probably as aluminum and calcium sulphides. Under properly controlledconditions, there is no substantial loss of silicon incurred in thetreatment of the invention, and

In the practice of the invention the sulphide treatment is preferablycarried out in the ladle. Thus, a silicide or high silicon alloy isproduced in the 'usual way, and a part of it may then be tapped'into aladle. The desiredamount of sulphide is added to the material in theladle, and the remainder of the silicide or alloy is then tapped rapidlyto provide a stirring action. The molten material in the ladle isallowed to cool 10 to proper pouring temperature. The sulphide treatmentapparently raises the temperature-of the material in the ladle and alonger time is necessary for cooling than is necessary when no sulphideaddition is made, but this longer cool- 1 ing period is advantageousbecause it insures completion of the refining'action of the sulphidebefore pouring.

The following specific examples of the application of the method of theinvention to the refining of ferrosilicon illustrate the principles andpractice of the invention. It is to be understood, however, that theinvention is not limited to the treatment of ferrosilicon but is equallyapplicable to the refining of other high silicon alloys or silicides.

Two hundred and-fifty pounds of iron pyrites containing about 41% ironand 48% sulphur, the remainder principally silica, were added to theladle during the tapping of about 7500 pounds of ferrosilicon containing47.16% silicon, 1.5%

aluminum. 0.08% calcium, 0.003% sulphur, .re -ma1'nder principally iron.The molten ferrosili con was tapped rapidly to give a good stirringaction. The molten material'in the ladle Was- 'al1owed to cool to a lowpouring temperature and was then poured into chills. The ferrosiliconproduced contained 47.23% silicon, 1.07% aluminum, 0.006% sulphur andnil calcium. Thus,

- the silicon to aluminum ratio was improved from 40 31.4 to 1 to 44.2to 1, there was no loss of silicon,

no appreciable increase in sulphur content, and the calcium was entirelyeliminated.

In another test of the method of the invention 6500 pounds of-amoltenferrosilicon contain- I ing 50.65% silicon, 1.45% aluminum, 0.26%calcium, 0.005% sulphur, the remainder principally iron, were tappedinto a ladle. A portion of the molten ferrosilic'on' was then pouredfrom this ladle into a second ladle and 275 pounds of iron pyritescontaining about 41% iron and 48% sulphur were rapidly added tothe smallportion of molten metal in the second ladle. The remain-' ingferrosilicon in the first ladle was then poured into the second ladle,the stream stirring the material already in the second ladle. After allof 1 2 asonaeo the ferrosilicon'had been poured into the second ladle,the contents or the second ladle were repoured into the first ladle toobtain further stirring. The molten metal was then allowed to cool topouring temperature and was then poured into chills. The productcontained 49.84% silicon, 0.73% aluminum, 0.02% calcium and 0.003%sulphur. Thus, by'the-"sulphide treatment the aluminum in theferrosilicon was decreased from 1.45% to 0.73%, the calcium wasdecreased from 0.26% to 0.02%, there was no increase in sulphur content.and the silicon content was not rail a lltially decreased.

' another test of the method of the invention 250 pounds oi ironpyrit'es of the same lot usedin the previous examples were added to aladle containing 7000 pounds of a ferrosilicon contain-'- a treatment orthe invention not only contain as aluminum and calcium than alloys or,silicides which have not been given this treatment, but the materialproduced is exceptionally sound and dense and is considerably tougherthan alloys or silicides which have not been given the treatment of theinvention. v

While specific examples have been given of the application of theinvention to the production of ierrosilicon these examples merelyillustrate the principles of the invention and the invention is notlimited to such examples. For instance, it may be used to advantage inthe treatment of nickel-silicon alloys, cobalt-silicon ing li.8%aluminum and 0.07% calcium. Jitter the writes-treatment the ferrosillconproduced contained'QBV; aluminum and 0.0l%.'calcium.

tent of the lei-rosilicon was reduced from 0.39%

to 0.19% and the calcium content was reduced from 0.06%150 0.04%.

it has been found that high silicon alloys or silicides which have beengiven the sulphide I alloys, and other high silicon alloys or silicides.

' I'claim:

l-. A process of purifying iron alloys containing a large proportion ofsilicon-and only small proportions of the impurities aluminum andcaloium which comprises subjecting a molten bath of such high siliconalloy1-t0 the action of a metallic sulphide. I e

2. A process of preparing ferrosilicon containing unobjectionableproportions of aluminumand calcium which comprises subjecting a moltenierrosilicon containing objectionable proportions oi such elements tothe action of iron sulphide.

3. A process of preparing a ferrosilicon comtaining unobjectionableproportions of aluminum and calcium as impurities which comprisesforming a molten 'bath of a ferro-silicon containin objectionableproportions of such elements and adding to such bath a quantity of ironsulphide, sumcient to remove at least a portion of the aluminum andcalcium present in said ferrosilicon.

JOSEPH H. BRENNAN.

